Semiconductor packages having a dam structure

ABSTRACT

A semiconductor package is disclosed. The disclosed semiconductor package includes a substrate having bonding pads at an upper surface thereof, a lower semiconductor chip, at least one upper semiconductor chip disposed on the lower semiconductor chip, and a dam structure having a closed loop shape surrounding the lower semiconductor chip. The dam structure includes narrow and wide dams disposed between the lower semiconductor chip and the bonding pads. The wide dam has a greater inner width than the narrow dam. The semiconductor packages further includes an underfill disposed inside the dam structure and being filled between the substrate and the lower semiconductor chip.

CROSS-REFERENCE TO THE RELATED APPLICATION

This U.S. nonprovisional application is a continuation of U.S. patent application Ser. No. 16/928,159, filed Jul. 14, 2020, in the U.S. Patent and Trademark Office, which claims the benefit of priority under 35 U.S.C. § 119 from Korean Patent Application No. 10-2020-0012460, filed on Feb. 3, 2020, in the Korean Intellectual Property Office, the entire contents of both of which are incorporated herein by reference.

BACKGROUND 1. Field

The example embodiments of the disclosure relate to a semiconductor package having a dam structure.

2. Description of the Related Art

To cope with a tendency of semiconductor devices toward miniaturization, a technology for mounting semiconductor chips having individual functions in a single semiconductor package is required. Such a semiconductor package includes an underfill configured to be filled between a substrate and a lower semiconductor chip, and a dam structure configured to prevent bonding pads from being covered by the underfill. In the case in which the size of the semiconductor package is reduced, there may be a problem in that a dispensing area of the underfill may be narrowed.

SUMMARY

The example embodiments of the disclosure provide a semiconductor package including a dam structure having a narrow dam and a wide dam.

According to some example embodiments, a semiconductor package may include a substrate having bonding pads at an upper surface thereof, a lower semiconductor chip disposed on the substrate and at least one upper semiconductor chip disposed on the lower semiconductor chip, a dam structure disposed on the substrate and having a closed loop shape surrounding the lower semiconductor chip, the dam structure including narrow and wide dams, the narrow dam being disposed between the lower semiconductor chip and the bonding pads, and the wide dam having a greater inner width than the narrow dam, and an underfill disposed inside the dam structure and being filled between the substrate and the lower semiconductor chip.

According to some example embodiments, a semiconductor package may include a substrate having bonding pads at an upper surface thereof, a lower semiconductor chip disposed on the substrate and at least one upper semiconductor chip disposed on the lower semiconductor chip, an underfill filled between the substrate and the lower semiconductor chip, the underfill including a non-extension portion disposed between the lower semiconductor chip and the bonding pads, and an extension portion having a greater width than the non-extension portion, and a dam structure disposed on the substrate and having a closed loop shape surrounding the underfill.

According to some example embodiments, a semiconductor package may include a substrate having bonding pads at an upper surface thereof, a lower semiconductor chip mounted on the substrate by flip-chip bonding and an upper semiconductor chip mounted on the lower semiconductor chip by wire bonding, an external connection terminal disposed beneath the substrate, a dam structure disposed on the substrate and having a closed loop shape surrounding the lower semiconductor chip, the dam structure including narrow and wide dams, the narrow dam being disposed between the lower semiconductor chip and the bonding pads, and the wide dam having a greater inner width than the narrow dam, an underfill disposed inside the dam structure and being filled between the substrate and the lower semiconductor chip, and an encapsulant covering the substrate, the lower semiconductor chip, and the upper semiconductor chip.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of inventive concepts will become more apparent to those of ordinary skill in the art by describing example embodiments thereof in detail with reference to the accompanying drawings, in which like numbers refer to like elements throughout. In the drawings:

FIG. 1 is a plan view of a semiconductor package, according to an example embodiment of the inventive concepts.

FIG. 2A to 2C are vertical cross-sectional views of the semiconductor package shown in FIG. 1 , respectively taken along lines I-I′, and

FIG. 3 is a plan view of a semiconductor package, according to an example embodiment of the inventive concepts.

FIG. 4 is a plan view of a semiconductor package, according to an example embodiment of the inventive concepts.

FIG. 5 is a vertical cross-sectional view of the semiconductor package shown in FIG. 4 , taken along line IV-IV′.

FIG. 6 is a plan view of a semiconductor package, according to an example embodiment of the inventive concepts.

FIGS. 7 to 12 are plan views and vertical cross-sectional views illustrating in a process order a method of manufacturing a semiconductor package, according to an example embodiment of the inventive concepts.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 is a plan view of a semiconductor package, according to an example embodiment of the inventive concepts.

FIG. 2A to 2C are vertical cross-sectional views of the semiconductor package shown in FIG. 1 , respectively taken along lines I-I′, II-II′ and III-III′.

Referring to FIG. 1 and FIGS. 2A to 2C, a semiconductor package, which is designated by reference numeral “100”, may include a substrate 102, a dam structure D, a lower semiconductor chip 110, an underfill 120, an upper semiconductor chip 130, an encapsulant 140, and external connection terminals 150.

The substrate 102 may include upper pads 104 disposed at an upper surface of the substrate 102. The substrate 102 may also include lower pads 106 disposed at a lower surface of the substrate 102. The upper pads 104 may be electrically connected to corresponding ones of the lower pads 106, respectively. In addition, the substrate 102 may include bonding pads 108 disposed at the upper surface of the substrate 102. Upper surfaces of the bonding pads 108 may be coplanar with the upper surface of the substrate 102. The bonding pads 108 may be electrically connected to corresponding ones of the lower pads 106, respectively. The bonding pads 108 may be disposed at three sides of the substrate 102. For example, the bonding pads 108 may be disposed at one lateral edge of the substrate 102 extending in a first horizontal direction x and opposite lateral edges of the substrate 102 extending in a second horizontal direction y, when viewed in a plan view, but embodiments of the disclosure are not limited thereto. Although the bonding pads 108 are illustrated as having a rectangular shape, in some example embodiments, the bonding pads 108 may have a circular shape, an oval shape, or other shapes.

The lower semiconductor chip 110 may be disposed on the substrate 102. The lower semiconductor chip 110 may have a rectangular shape and, as such, may have a first side surface 111, a second side surface 112, a third side surface 113, and a fourth side surface 114. The lower semiconductor chip 110 may include bumps 116 disposed at a lower surface of the lower semiconductor chip 110. Each bump 116 may contact the upper surface of a corresponding one of the upper pads 104. The bumps 116 may be electrically connected to the substrate 102 via the upper pads 104, respectively.

The dam structure D may be disposed at the upper surface of the substrate 102 and may surround the lower semiconductor chip 110. For example, the dam structure D may extend around the first side surface 111, the second side surface 112, the third side surface 113, and the fourth side surface 114 of the substrate 102. The dam structure D may include a narrow dam Da, a wide dam Db, a first connector Dc1, and a second connector Dc2. The narrow dam Da may be disposed between the bonding pads 108 and the lower semiconductor chip 110. The narrow dam Da may have a relatively small inner width in the second horizontal direction y. The wide dam Db may be connected to the narrow dam Da and may have a relatively large inner width in the second horizontal direction y. In an example embodiment, the distance between the lower semiconductor chip 110 and the wide dam Db may be greater than the distance between the lower semiconductor chip 110 and the narrow dam Da. For example, the distance between the lower semiconductor chip 110 and the narrow dam Da, that is, a distance W1, may be 200 to 400 μm, and the distance between the lower semiconductor chip 110 and the wide dam Db, that is, a distance W2, may be 500 to 1,000 μm. The distance between the segment of the narrow dam Da that extends lengthwise in the second horizontal direction y and the bonding pads 108 adjacent thereto in the first horizontal direction x, that is, a distance W3, may be 50 to 150 μm. In addition, a distance between the segments of the narrow dam Da that extend lengthwise in the first horizontal direction x and the bonding pads 108 adjacent thereto in the second horizontal direction y may be 50 to 150 μm. The distance between the wide dam Db and each of the first side surface 111, the third side surface 113, and the fourth side surface 114 of the substrate 102, that is, a distance W4, may be 100 to 300 μm. The distance between each of the first and second connectors Dc1 and Dc2 and the bonding pad 108 disposed adjacent thereto in the first horizontal direction x, that is, a distance W5, may be 50 to 150 μm.

The dam structure D may spatially separate the bonding pads 108 and the underfill 120 from each other, forming a barrier between the bonding pads 108 and the underfill 120. For example, the narrow dam Da of the dam structure D may extend along the first to third side surfaces 111, 112, and 113 of the lower semiconductor chip 110 between the bonding pads 108 and the underfill 120.

In an example embodiment, each of the narrow dam Da and the wide dam Db may comprise linear segments that form a ⊏-shape or an angular C-shape. For example, the narrow dam Da may include three segments that are adjacent to and surround the first to third side surfaces 111, 112, and 113 of the lower semiconductor chip 110, and the wide dam Db may include three segments that are adjacent to and surround the first, third, and fourth side surfaces 111, 113, and 114 of the lower semiconductor chip 110. Each of the linear segments of the narrow dam Da may be positioned between a corresponding side surface of the lower semiconductor chip 110 and the bonding pads 108 adjacent thereto. When viewed in a plan view, the narrow dam Da and the wide dam Db may include a first end Da1 and a first end Db1, which are disposed adjacent to the first side surface 111 of the lower semiconductor chip 110, respectively, and a second end Da2 and a second end Db2, which are disposed adjacent to the third side surface 113 of the lower semiconductor chip 110, respectively. The first connector Dc1 may connect the first end Da1 and the first end Db1. The second connector Dc2 may connect the second end Da2 and the second end Db2. In some example embodiments, each of the narrow dam Da and the wide dam Db may have a round C-shape or an arc shape. The distance W5 between each of the first and second connectors Dc1 and Dc2 and the bonding pad 108 disposed adjacent thereto in the first horizontal direction x may be 50 to 150 μm. The bonding pads 108 may be disposed to face corresponding ones of the first to third side surfaces 111, 112, and 113 of the lower semiconductor chip 110.

The underfill 120 may be filled between the substrate 102 and the lower semiconductor chip 110. The underfill 120 may include an epoxy resin. The underfill 120 may protect the bumps 116. The underfill 120 may partially cover the upper surface of the substrate 102, and may not cover the bonding pads 108. The underfill 120 may be disposed inside the dam structure D, and may contact an inner surface of the dam structure D. For example, the underfill 120 may be disposed within a perimeter formed by the dam structure D.

When viewed in a plan view, the underfill 120 may include a non-extension portion 120 a filling an area inside the narrow dam Da, and an extension portion 120 b filling an area inside the wide dam Db. The non-extension portion 120 a may be disposed between the bonding pads 108 and the lower semiconductor chip 110. The extension portion 120 b may be connected to the non-extension portion 120 a. The extension portion 120 b may have a greater width in the second horizontal direction y than the non-extension portion 120 a in the second horizontal direction y. For example, the distance between the lower semiconductor chip 110 and a side surface of the extension portion 120 b in the second horizontal direction y (e.g., the side surface of the extension portion 120 b that contacts an inner surface of the wide dam Db) may be greater than the distance between the lower semiconductor chip 110 and a side surface of the non-extension portion 120 a in the second horizontal direction y (e.g., the side surface of the non-extension portion 120 a that contacts an inner surface of the narrow dam Da). Although each of the non-extension portion 120 a and the extension portion 120 b is illustrated as having a rectangular shape, each of the non-extension portion 120 a and the extension portion 120 b may have a circular shape or an oval shape without being limited thereto.

The amount of the underfill 120 filled between the substrate 102 and the lower semiconductor chip 110 may be dependent on the height of the bumps 116. However, when the size of the semiconductor package 100 is reduced, the dispensing area of the underfill 120 may be insufficient. Since the semiconductor package 100 according to the example embodiment of the inventive concepts includes the dam structure D having the narrow dam Da and the wide dam Db, it may be possible to secure a relatively wide dispensing area of the underfill 120 for a given size of the semiconductor package 100.

The upper semiconductor chip 130 may be disposed on the lower semiconductor chip 110. In an example embodiment, the upper semiconductor chip 130 may be mounted on the substrate 102 by wire bonding. For example, the upper semiconductor chip 130 may include chip pads 132 disposed on an upper surface of the upper semiconductor chip 130. The bonding pads 108 of the substrate 102 and the chip pads 132 of the upper semiconductor chip 130 may be electrically connected by bonding wires 134, respectively. The upper semiconductor chip 130 may be fixed to an upper surface of the lower semiconductor chip 110 by an adhesive 136.

The lower semiconductor chip 110 may include an application processor (AP) such as a microprocessor or a microcontroller, or a logic chip such as a central processing unit (CPU), a graphics processing unit (GPU), a modem, an application-specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The upper semiconductor chip 130 may include a volatile memory such as dynamic random access memory (DRAM) or a non-volatile memory such as a flash memory. In an example embodiment, the lower semiconductor chip 110 may include a modem chip, and the upper semiconductor chip 130 may include a DRAM chip.

The encapsulant 140 may cover the substrate 102, the lower semiconductor chip 110, the upper semiconductor chip 130, and the dam structure D. In some embodiments, the encapsulant 140 may cover an upper surface of the underfill 120 between the lower semiconductor chip 110 and the dam structure D. In an example embodiment, the encapsulant 140 may include an epoxy molding compound (EMC).

The external connection terminals 150 may be formed at the lower surface of the substrate 102. The external connection terminals 150 may be connected to the lower pads 106 of the substrate 102, respectively, and, as such, may be electrically connected to the upper pads 104 via the lower pads 106, respectively.

FIG. 3 is a plan view of a semiconductor package, according to an example embodiment of the inventive concepts.

Referring to FIG. 3 , a semiconductor package, which is designated by reference numeral “200”, may include a dam structure D disposed on a substrate 102 and surrounding a lower semiconductor chip 110. The semiconductor package 200 may include alignment marks 208 disposed on the substrate 102. The alignment marks 208 may serve as a reference for alignment of an upper semiconductor chip 130 on the substrate 102 and connection of the upper semiconductor chip 130 to bonding pads 108 upon disposition of the upper semiconductor chip 130. The alignment marks 208 may be disposed at an edge of the substrate 102. For example, two alignment marks 208 may be disposed at two corners of the substrate 102 opposite to each other in a diagonal direction, respectively.

The dam structure D may not overlap with the alignment marks 208. For example, the dam structure D may include a cutout C bent at a right angle to face a corresponding one of the alignment marks 208. The cut-out C may be disposed to be spaced apart from the corresponding alignment mark 208. As such, the alignment marks 208 may be disposed outside the dam structure D.

FIG. 4 is a plan view of a semiconductor package, according to an example embodiment of the inventive concepts.

FIG. 5 is a vertical cross-sectional view of the semiconductor package shown in FIG. 4 , taken along line IV-IV′.

Referring to FIGS. 4 and 5 , a semiconductor package, which is designated by reference numeral “300”, may include a dam structure D surrounding a lower semiconductor chip 110, and an underfill 320 disposed inside the dam structure D. A first upper semiconductor chip 330 a and a second upper semiconductor chip 330 b may be disposed on the lower semiconductor chip 110. The first upper semiconductor chip 330 a and the second upper semiconductor chip 330 b may be disposed to be spaced apart from each other in a first horizontal direction x. In an example embodiment, the first upper semiconductor chip 330 a and the second upper semiconductor chip 330 b may be mounted on a substrate 102 by wire bonding. The first upper semiconductor chip 330 a may include first chip pads 332 a disposed at an upper surface of the first upper semiconductor chip 330 a. The second upper semiconductor chip 330 b may include second chip pads 332 b disposed at an upper surface of the second upper semiconductor chip 330 b. The first chip pads 332 a may be disposed to form a ⊏-shape. For example, the first chip pads 332 a may be disposed at upper, lower, and left sides of the first upper semiconductor chip 330 a, and not disposed on a right side of the first upper semiconductor chip 330 a. The second chip pads 332 b may be disposed to form a ⊏-shape. For example, the second chip pads 332 b may be disposed at upper, lower, and right sides of the second upper semiconductor chip 330 b, and not disposed on a left side of the second upper semiconductor chip 330 b. The bonding pads 108 may be disposed to surround the lower semiconductor chip 110 such that the bonding pads 108 correspond to the first chip pads 332 a and the second chip pads 332 b, respectively.

The dam structure D may include a narrow dam Da and a wide dam Db. For example, the dam structure D may include two narrow dams Da spaced apart from each other in the first horizontal direction x, and two wide dams Db disposed between the narrow dams Da and extending in the second horizontal direction y. A width in the first horizontal direction x of the wide dams Db may be greater than the distance between the first upper semiconductor chip 330 a and the second upper semiconductor chip 330 b. The narrow dams Da may extend between the bonding pads 108 and the lower semiconductor chip 110. The dam structure D may surround the lower semiconductor chip 110, and may have a closed loop shape.

The underfill 320 may be disposed inside the dam structure D, and may contact an inner surface of the dam structure D. When viewed in a plan view, the underfill 320 may include non-extension portions 320 a respectively filling areas inside the narrow dams Da, and extension portions 320 b respectively filling areas inside the wide dams Db. The extension portions 320 b may have a greater width than the non-extension portions 320 a. For example, the width of the extension portions 320 b between a side surface of the lower semiconductor chip 120 and an inner surface of the wide dam Db in the second horizontal direction y may be greater than the width of the non-extension portions 320 a between a side surface of the lower semiconductor chip 120 an inner surface of the narrow dam Da in the second horizontal direction y.

FIG. 6 is a plan view of a semiconductor package according to an example embodiment of inventive concepts.

Referring to FIG. 6 , a semiconductor package 400 may include a dam structure D surrounding a lower semiconductor chip 110, and an underfill 420 disposed inside the dam structure D. An upper semiconductor chip 130 may include chip pads 432 disposed at an upper surface of the upper semiconductor chip 130. The chip pads 432 may be disposed at left and right edges of the upper semiconductor chip 130. Bonding pads 108 may be disposed at left and right edges of a substrate 102 while corresponding to the chip pads 432, respectively.

The dam structure D may include a narrow dam Da and a wide dam Db. For example, when viewed in a plan view, the dam structure D may include a narrow dam Da, and a wide dam Db disposed beneath the narrow dam Da. The narrow dam Da may have an internal width that is narrower in the first horizontal direction x than an internal width of the wide dam Db in the first horizontal direction x. The narrow dam Da may extend between the bonding pads 108 and the lower semiconductor chip 110. The dam structure D may surround the lower semiconductor chip 110, and may have a closed loop shape.

When viewed in a plan view, the underfill 420 may include a non-extension portion 420 a filling an area inside the narrow dam Da, and an extension portion 420 b filling an area inside the wide dam Db.

FIGS. 7 to 12 are plan views and vertical cross-sectional views illustrating a process order of a method of manufacturing a semiconductor package, according to an example embodiment of the inventive concepts. FIGS. 7, 9, and 11 are plan views explaining the method for manufacturing the semiconductor package 100. FIGS. 8, 10, and 12 are cross-sectional views taken along line I-I′ in FIGS. 7, 9, and 11 , respectively.

Referring to FIGS. 7 and 8 , a substrate 102 may be provided. The substrate 102 may include upper pads 104 disposed at the upper surface of the substrate 102. The substrate 102 may include lower pads 106 disposed at the lower surface of the substrate 102. The upper pads 104 may be electrically connected to corresponding ones of the lower pads 106, respectively. In addition, the substrate 102 may include bonding pads 108 disposed at the upper surface of the substrate 102. The upper pads 104, the lower pads 106, and the bonding pads 108 may include metal such as Al, Ti, Cr, Fe, Co, Ni, Cu, Zn, Pd, Pt, Au and Ag.

Referring to FIGS. 9 and 10 , a dam structure D may be formed at the upper surface of the substrate 102. A lower surface of the dam structure D may contact the upper surface of the substrate 102. The dam structure D may include a photoresist resin or metal such as Al or Cu. In an example embodiment, the dam structure D may include a photoresist resin. The photoresist resin may include an epoxy resin, an acrylic monomer, a phosphine oxide compound, an amine compound, silica, barium sulfate, or the like.

The dam structure D may be formed by forming a photoresist resin layer over the upper surface of the substrate 102, and then etching the photoresist resin layer. The dam structure D may have an upper surface that is planar and parallel to the upper surface of the substrate 102, and side surfaces that are planar and perpendicular to the upper surface of the substrate 102. In an example embodiment, the dam structure D may have a height of 18 μm or less. As used herein, height may refer to the thickness of height measured in a direction perpendicular to the upper surface of the substrate 102. The height of the dam structure D may be equal to or less than a distance between the upper surface of the substrate 102 and a lower surface of the lower semiconductor chip 110. The dam structure D may be disposed to surround the upper pads 104, and may have a closed loop shape. The upper pads 104 may be disposed inside the closed loop of the dam structure D, whereas the bonding pads 108 may be disposed outside the closed loop of the dam structure D. The dam structure D may include a narrow dam Da, a wide dam Db, and a first connector Dc1 and a second connector Dc2, which connect the narrow dam Da and the wide dam Db. For example, each of the narrow dam Da and the wide dam Db may have a ⊏-shape or an angular C-shape. A first end Da1 of the narrow dam Da may be connected to a first end Db1 of the wide dam Db by the first connector Dc1. A second end Da2 of the narrow dam Da may be connected to a second end Db2 of the wide dam Db by the second connector Dc2. In some embodiments, each of the first connector Dc1 and the second connector Dc2 may be perpendicular to the segments of the narrow dam Da and the wide dam Db to which they are connected. In an example embodiment, the distance between the narrow dam Da and the corresponding side surface of the substrate 102 may be greater than the distance between the wide dam Db and the corresponding side surface of the substrate 102.

Referring to FIGS. 11 and 12 , a lower semiconductor chip 110 may be mounted on the substrate 102. In addition, an underfill 120 may be formed. The lower semiconductor chip 110 may be mounted on the substrate 102 by flip-chip bonding. The lower semiconductor chip 110 may have a rectangular shape and, as such, may have a first side surface 111, a second side surface 112, a third side surface 113, and a fourth side surface 114. The lower semiconductor chip 110 may include the bumps 116 disposed at the lower surface of the lower semiconductor chip 110 while being connected to the upper pads 104, respectively.

After mounting of the lower semiconductor chip 110, the underfill 120 may be formed to be filled between the substrate 102 and the lower semiconductor chip 110. In an example embodiment, the underfill 120 may include an epoxy resin. The underfill 120 may be formed inside the dam structure D, and may not cover the bonding pads 108. The underfill 120 may be formed using a dispensing method. For example, the underfill 120 may be supplied from a dispenser 122 to an area between the fourth side surface 114 of the lower semiconductor chip 110 and the dam structure D. The underfill 120 may be filled between the substrate 102 and the lower semiconductor chip 110 while flowing from the fourth side surface 114 toward the second side surface 112.

Referring back to FIG. 1 and FIGS. 2A to 2C, an upper semiconductor chip 130 may be disposed on the lower semiconductor chip 110. The upper semiconductor chip 130 may be mounted on the substrate 102 by wire bonding. For example, chip pads 132 of the upper semiconductor chip 130 may be connected to the bonding pads 108 by bonding wires 134, respectively. The upper semiconductor chip 130 may be fixed to the upper surface of the lower semiconductor chip 110 by an adhesive 136. The adhesive 136 may include a die attach film (DAF) or an epoxy resin.

An encapsulant 140 may be formed to cover the substrate 102, the lower semiconductor chip 110, the upper semiconductor chip 130, and the dam structure D. The encapsulant 140 may be a resin including epoxy, polyimide, or the like. For example, the encapsulant 140 may include a bisphenol-group epoxy resin, a polycyclic aromatic epoxy resin, an o-cresol novolac epoxy resin, a biphenyl-group epoxy resin, a naphthalene-ground epoxy resin, or the like.

In accordance with the example embodiments of the disclosure, it may be possible to secure a wide dispensing area of an underfill through a configuration in which a dam structure includes a narrow dam and a wide dam.

While the embodiments of the disclosure have been described with reference to the accompanying drawings, it should be understood by those skilled in the art that various modifications may be made without departing from the scope of the disclosure and without changing essential features thereof. Therefore, the above-described embodiments should be considered in a descriptive sense only and not for purposes of limitation. 

1.-20. (canceled)
 21. A semiconductor package, comprising: a substrate having first and third sides opposing each other and second and fourth sides connecting the first and third sides, the substrate including bonding pads adjacent to the first side, the second side, and the fourth side, and upper pads farther from the first side, the second side, and the fourth side than the bonding pads; a lower semiconductor chip disposed on the substrate, and electrically connected to the upper pads by bumps, the lower semiconductor chip having first side surface opposing the first side of the substrate, second side surface opposing the second side of the substrate, third side surface opposing the third side of the substrate, and fourth side surface opposing the fourth side of the substrate; at least one upper semiconductor chip disposed on the lower semiconductor chip, and electrically connected to the bonding pads by bonding wires; a dam structure including a first dam and a second dam, connected to each other and surrounding the lower semiconductor chip in a single closed loop shape on the substrate; and an underfill disposed inside the dam structure, wherein the second side and the fourth side each have a first portion adjacent to the bonding pads and a second portion, other than the first portion, wherein the first dam is spaced apart from each of the first side surface, the second side surface, and the fourth side surface by a first distance between the first side of the substrate and the first side surface of the lower semiconductor chip, between the first portion of the second side of the substrate and the second side surface of the lower semiconductor chip, and between the first portion of the fourth side of the substrate and the fourth side surface of the lower semiconductor chip, and wherein the second dam is spaced apart from each of the second side surface, and the fourth side surface by a second distance, greater than the first distance, between the second portion of the second side of the substrate and the second side surface of the lower semiconductor chip, and between the second portion of the fourth side of the substrate and the fourth side surface of the lower semiconductor chip.
 22. The semiconductor package as claimed in claim 21, wherein the bonding pads are positioned inside the single closed loop shape.
 23. The semiconductor package as claimed in claim 21, wherein the upper pads are positioned outside of the single closed loop shape.
 24. The semiconductor package as claimed in claim 21, wherein the first distance ranges about 200 μm to about 400 μm.
 25. The semiconductor package as claimed in claim 21, wherein the second distance ranges about 500 μm to about 1000 μm.
 26. The semiconductor package as claimed in claim 21, wherein a third distance between the first dam and the bonding pads ranges about 50 μm to about 150 μm.
 27. The semiconductor package as claimed in claim 21, wherein a fourth distance between the second dam and the second portion of each of the second side and fourth side ranges about 100 μm to about 300 μm.
 28. The semiconductor package as claimed in claim 21, wherein the dam structure further includes a connector connecting an end of the first dam and an end of the second dam.
 29. The semiconductor package as claimed in claim 28, wherein a fifth distance between the connector and an adjacent one of bonding pads ranges about 50 μm to about 150 μm.
 30. The semiconductor package as claimed in claim 21, wherein the bonding pads are not disposed adjacently to the third side of the substrate, and wherein the second dam is further disposed between the third side of the substrate and the third side surface of the lower semiconductor chip.
 31. The semiconductor package as claimed in claim 21, further comprising an alignment mark disposed on the substrate and outside of the single closed loop shape.
 32. The semiconductor package as claimed in claim 31, wherein the dam structure includes a cut-out bent to face the alignment mark.
 33. The semiconductor package as claimed in claim 21, wherein the bonding pads are further disposed adjacent to the third side of the substrate, and wherein the first dam is further disposed between the third side of the substrate and the third side surface of the lower semiconductor chip.
 34. A semiconductor package, comprising: a substrate having a pair of first sides opposing each other and a pair of second sides connecting the pair of first sides, the substrate including bonding pads adjacent to the pair of first sides, and upper pads farther from the pair of first sides than the bonding pads; a lower semiconductor chip disposed on the substrate, and electrically connected to the upper pads by bumps, the lower semiconductor chip having a pair of first side surfaces opposing the pair of first sides of the substrate, and a pair of second side surfaces opposing the pair of second sides of the substrate; at least one upper semiconductor chip disposed on the lower semiconductor chip, and electrically connected to the bonding pads by bonding wires; a dam structure including a first dam and a second dam that are connected to each other and surround the lower semiconductor chip in a single closed loop shape on the substrate; and an underfill disposed inside the dam structure, wherein each of the pair of first sides has a first portion adjacent to the bonding pads and a second portion other than the first portion, wherein the first dam is spaced apart from each of the pair of first side surfaces of the lower semiconductor chip by a first distance between the first portion of the pair of first sides of the substrate and the pair of first side surfaces of the lower semiconductor chip, and wherein the second dam is spaced apart from each of the pair of first side surfaces of the lower semiconductor chip by a second distance, greater than the first distance, between the second portion of the pair of first sides of the substrate and the pair of first side surfaces of the lower semiconductor chip.
 35. The semiconductor package as claimed in claim 34, wherein the bonding pads are not disposed adjacently to the pair of second sides of the substrate, and wherein the second dam is further disposed between the pair of second sides of the substrate and the pair of second side surfaces of the lower semiconductor chip.
 36. A semiconductor package comprising: a substrate having bonding pads at an upper surface thereof; a lower semiconductor chip disposed on the substrate and at least one upper semiconductor chip disposed on the lower semiconductor chip; an underfill filled between the substrate and the lower semiconductor chip, the underfill including a non-extension portion disposed between the lower semiconductor chip and the bonding pads, and an extension portion having a greater width than the non-extension portion; and a dam structure disposed on the substrate and having a closed loop shape surrounding the underfill.
 37. The semiconductor package as claimed in claim 36, wherein a distance between the lower semiconductor chip and a side surface of the extension portion is greater than a distance between the lower semiconductor chip and a side surface of the non-extension portion.
 38. The semiconductor package as claimed in claim 36, wherein: the dam structure includes narrow and wide dams, the narrow dam being disposed between the lower semiconductor chip and the bonding pads, and the wide dam having a greater inner width than the narrow dam; the narrow dam surrounds the non-extension portion; and the wide dam surrounds the extension portion.
 39. The semiconductor package as claimed in claim 36, wherein the extension portion and the non-extension portion contact an inner surface of the dam structure.
 40. The semiconductor package as claimed in claim 36, wherein the dam structure spatially separates the underfill from the bonding pads. 